LCD device including a reflection film having a convex-concave surface

ABSTRACT

An LCD device includes a reflective area in each pixel. A reflection film having a convex-concave surface is provided in the reflective area, film in cross section configuration is formed. Each pixel includes a pixel electrode and a common electrode for applying a lateral electric field on a LC layer. The inclination angle of the reflection film has an inclination angle distribution, wherein the angle component in an area corresponding to the electrodes has a lower angle distribution than the angle components in an area corresponding to a gap between adjacent two of the electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/014,528 filed Jan. 15, 2008 which claims priority based onJapanese Patent Application No. 2007-008498 filed Jan. 17, 2007. Theentire disclosures of the prior applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an LCD device, and more particularly, to anLCD device of the reflective type or transflective type of thelateral-electric-field drive mode.

2. Description of the Related Art

Conventionally, there have been suggested LCD devices of reflective typeor transflective type in which a pixel electrode and a common electrodeare formed on the same substrate, as in an IPS mode or FFS mode, and LCmolecules are switched using a lateral electric field generated betweenthe pixel electrode and the common electrode to thereby display an imageon the screen. For example, in Patent Publications JP-2003-344837A1,JP-2005-338256A1, there have been described transflective typelateral-electric-field drive modes using a reflection mode as a normallyblack mode under which absence of applied voltage on the LC layerrepresents a dart state or black. Furthermore, in JP-2006-180200A, therehas been described a transflective type lateral-electric-field drivemode using a reflection mode as a normally white mode under whichabsence of applied voltage on the LC layer represents a bright state orwhite.

Hereinafter, a transflective type LCD device of thelateral-electric-field drive mode described in JP-2003-344837A1 will bedescribed. FIG. 25 shows a schematic sectional view indicative of an LCDdevice described in this publication. The LCD device 200 includes a pairof substrates including TFT substrate 214 and counter substrate 212,which oppose each other, an LC layer 213 which is sandwiched between theTFT substrate 214 and the counter substrate 212, and polarizing films211, 215 which are attached to the external surfaces of the TFTsubstrate 214 and counter substrate 212, respectively, far from the LClayer 213. Between the LC layer 213 and the polarizing film 215, ahalf-wave (λ/2) plate 218 is inserted. In FIG. 25, the LCD device 200has a backlight unit (not shown) that irradiates backlight to the LClayer 213 through the polarizing film 215. Furthermore, on the surfaceof the TFT substrate 214 and counter substrate 212 near the LC layer213, a horizontal orientation film (not shown) is formed. The angleformed between the orientation directions of the two horizontalorientation films represents a twist angle of the LC layer 213.

The LCD device 200 includes in each pixel a transmissive area 222 thatallows the light incident from the backlight unit to transmit from thepolarizing film 215 toward the polarizing film 211, to thereby displayan image on the screen, and a reflective area 221 that reflects thelight incident from the outside through the polarizing film 211 andreflected by a reflection film 216, to thereby display an image on thescreen. A first insulating film 217 is formed on the surface of the TFTsubstrate 214 near the LC layer 213. In the reflective area 221, asecond insulating film 242 is formed on the first insulating film 217,and the reflection film 216 is formed thereon. On the reflection film216, a third insulating film 241 is formed, and on the third insulatingfilm 241, lateral-electric-field drive electrodes including pixelelectrode 235 and common electrode 237 are formed. On the other hand, inthe transmissive area 222, lateral-electric-field drive electrodesincluding pixel electrode 236 and common electrode 238 are formed on thefirst insulating film 217 arranged on the TFT substrate 214.

In the reflective area 221, the pixel electrode 235 and common electrode237 extend parallel to each other, and the LC layer 213 is driven by alateral electric field generated between the pixel electrode 235 and thecommon electrode 237. In the transmissive area 222 either, the pixelelectrode 236 and common electrode 238 extend parallel to each other,and the LC layer 213 is driven by a lateral electric field generatedbetween the pixel electrode 236 and the common electrode 238. The secondinsulating film 242 and third insulating film 241 adjust the differencebetween the LC cell gap of the reflective area 221 and the LC cell gapof the transmissive area 222. Specifically, when the gap of the LC layer213 in the transmissive area 222 is set to ½ wavelength (λ/2) of light,the gap of the LC layer 213 in the reflective area 221 is adjusted to ¼wavelength.

FIG. 26A shows the polarizing axis direction of the polarizing film 211and the LC orientation direction in the LC layer 213 of theabove-described LCD device, and FIG. 26B shows the polarized state oflight in the reflective area 221. It is defined, as shown in FIG. 26A,that the polarizing axis of the polarizing film 211 and the LCorientation direction in the LC layer 213 is at 90 degrees. In thisnotation, as shown in FIG. 26A, upon absence of applied voltage on theLC layer, a 90-degree-linearly polarized light passed by the polarizingfilm 211 directly passes through the LC layer 213, and is reflected bythe reflection film 216 with its polarized state being kept linearlypolarized. The reflected linearly polarized light directly passesthrough the LC layer 213, and passes by the polarizing film 211, wherebythe image on the screen assumes a bright state or white. Upon presenceof applied voltage on the LC layer, the oriented angle of the LC layer213 assumes 45 degrees, and the linearly polarized light passed by thepolarizing film 211 passes through the LC layer 213 to assumeclockwise-circularly polarized light, which is reflected by thereflection film 216 to assume counterclockwise-circularly polarizedlight to pass through the LC layer 213, and advances toward thepolarizing film 211, as a 0-degree-linearly polarized light.Accordingly, the light is blocked by the polarizing film 211, wherebythe image on the screen represents a dark state or white, resulting in anormally white mode.

FIG. 27A shows another example of the polarizing axis direction of thepolarizing film 211 and the LC orientation direction in the LC layer 213of the above-described LCD device, and FIG. 27B shows the polarizedstate of light in the reflective area 221. As shown in FIG. 27A, a caseis considered in which the polarizing axis of the polarizing film 211 isset to 90 degrees, and the LC orientation direction in the LC layer 213is set to 45 degrees. In this case, upon absence of applied voltage, the90-degree-linearly polarized light passed by the polarizing film 211passes through the LC layer 213 to assume a clockwise-circularlypolarized light, which is reflected by the reflection film 216 to assumea counterclockwise-circularly polarized light. Since thecounterclockwise-circularly polarized light passes through the LC layer213 to assume a 0-degree-linearly polarized light, the light is blockedby the polarizing film 211, thereby representing a dark state or black.Upon presence of applied voltage, the oriented angle of the LC layer 213assumes 0 degree, and the 90-degree-linearly polarized light passed bythe polarizing film 211 passes through the LC layer 213 to be reflectedby the reflection film 216 with the polarized angle being kept at 90degrees. The reflected light from the reflection film 216 passes throughthe LC layer 213 with its polarized state being kept 90-degree-linearlypolarized, and is emitted from the polarizing film 211, whereby theimage on the screen represents a bright state or black, representing anormally black mode.

FIG. 28 shows the oriented state of LC molecules in the LCD device shownin FIG. 25 upon presence of applied voltage. Upon presence of appliedvoltage, a lateral electric field is generated between comb teethelectrodes, or between pixel electrode 235 and common electrode 237, andLC molecules in the LC layer 213 are oriented along the direction of thelateral electric field. However, since the lateral electric field is notapplied to the LC layer 213 on the comb teeth electrodes, the LCmolecules do not rotate thereon. More specifically, if the LCD device200 is used as the normally white mode, the LC molecules on the combteeth electrodes 235, 237 do not rotate. Therefore, the image on theelectrodes 235, 237 stays “white” even when a voltage is applied to theLC layer, and the image assumes “black” only on the gap between theelectrodes 235, 237, which raises a problem of lowering of the contrastratio.

Specifically, when the configuration of a convex-concave surface of thereflection film 216 was uniform between the area overlapping the gap ofelectrodes and in the area overlapping the electrodes, even uponpresence of applied voltage, the image on the electrodes stays bright,and the contrast ratio was 3:1 or lower at the maximum. With respect tothe normally black mode, the LC molecules on the electrodes do notrotate similarly. Therefore, the image on the electrodes stayed “black”even when a voltage is applied to the LC layer, and the image assumed“white” only in the area overlapping the gap between the electrodes,which raises a problem of lowering the reflectance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to solve the aboveproblems to provide an LCD device of the reflective type ortransflective type of the lateral-electric-field drive mode, which iscapable of operating in a normally white mode while suppressingreduction of the contrast ratio and operating in a normally black modewhile suppressing reduction in the reflectance.

It is another object of the present invention to provide a method formanufacturing the above LCD device, and a photomask to be used forforming a reflection film in the LCD device.

The present invention provides, in a first aspect thereof, a liquidcrystal display (LCD) device including: a reflection area for reflectingincident light and provided in at least a part of a pixel; a reflectionfilm provided in the reflection area and having a convex-concavesurface; and a plurality of electrodes for driving therebetween liquidcrystal (LC) molecules in a lateral direction, wherein: an inclinationangle of the convex-concave surface has different components between afirst area overlapping the electrodes and a second area overlapping agap between adjacent two of the electrodes.

The present invention provides, in a second aspect thereof, a photomaskfor use in forming a liquid crystal ((LCD) device including a reflectionarea for reflecting incident light in at least a part of a pixel; areflection film provided in the reflection area and having aconvex-concave surface; and a plurality of electrodes for driving liquidcrystal (LC) molecules in a lateral direction, wherein the photomask isused for forming the convex-concave surface on the reflection film, andhas no convex-concave pattern in an area overlapping the electrodes.

The present invention provides, in a third aspect thereof, a photomaskfor use in forming a liquid crystal (LCD) device including a reflectionarea for reflecting incident light in at least a part of a pixel; areflection film provided in the reflection area and having aconvex-concave surface; and a plurality of electrodes for driving liquidcrystal (LC) molecules in a lateral direction, wherein the photomask isused for forming the convex-concave surface on the reflection film, andincludes a light shield pattern added in an area overlapping theelectrodes.

The present invention provides, in a fourth aspect thereof, a photomaskfor use in forming a liquid crystal (LCD) device including a reflectionarea for reflecting incident light in at least a part of a pixel; areflection film provided in the reflection area and having aconvex-concave surface; and a plurality of electrodes for driving liquidcrystal (LC) molecules in a lateral direction, wherein the photomask isused for forming the convex-concave surface on the reflection film, andincludes a gray-tone pattern or a half-tone pattern in an areaoverlapping the electrodes.

The present invention provides, in a fifth aspect thereof, method ofmanufacturing an LCD device operating in a lateral-electric-field drivemode, the method including: coating photosensitive resin on a substrate;exposing the photosensitive resin by using a photomask according to thepresent invention; developing the exposed photosensitive resin; burningthe developed photosensitive resin to form a convex-concave overcoatfilm; and forming a reflection film on the convex-concave overcoat film.

The above and other objects, features and advantages of the presentinvention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view of an LCD device according to a firstembodiment of the present invention, showing the reflective area on theelectrodes in a pixel;

FIG. 1B is a partial sectional view of the LCD device of FIG. 1A,showing definition of the areas of the reflection film and theinclination angle of the convex-concave surface of the reflection film;

FIG. 2 is a timing chart indicative of the drive signal waveforms of thepixel electrode and the common electrode;

FIG. 3 is a schematic view of the polarized state of light in areflective area;

FIG. 4 is a sectional view indicative of the travelling state of lightin the reflective area of the pixel in the LCD device;

FIG. 5 is a top plan view of the pattern of a photomask used to form aconvex-concave film;

FIG. 6 is a top plan view of the pattern of another photomask used toform a convex-concave film;

FIG. 7 is a top plan view of the pattern of another photomask used toform a convex-concave film;

FIG. 8 is a top plan view of the pattern of another photomask used toform a convex-concave film;

FIG. 9 is a schematic perspective view indicative of the definition forthe incident direction, received angle, and specular reflection angle oflight used of the evaluation of the characteristic of an LCD device.

FIG. 10 is a plan view indicative of an LCD device in a step of thefabrication process for a TFT substrate, and

FIG. 10A to FIG. 10C are sectional views taken along lines A-A′ to C-C′in FIG. 10;

FIG. 11 and FIGS. 11A to 11D show a subsequent step subsequent to thestep of FIG. 10 and FIGS. 10A to 10C, showing the subsequent stepsimilarly thereto.

FIG. 12 and FIGS. 12A to 12D show a subsequent step subsequent to thestep of FIG. 11 and FIGS. 11A to 11D, showing the subsequent stepsimilarly thereto.

FIG. 13 and FIGS. 13A to 13D show a subsequent step subsequent to thestep of FIG. 12 and FIGS. 12A to 12D, showing the subsequent stepsimilarly thereto.

FIG. 14 and FIGS. 14A to 14D show a subsequent step subsequent to thestep of FIG. 13 and FIGS. 13A to 13D, showing the subsequent stepsimilarly thereto.

FIG. 15 and FIGS. 15A to 15D show a subsequent step subsequent to thestep of FIG. 14 and FIGS. 14A to 14D, showing the subsequent stepsimilarly thereto.

FIG. 16 and FIG. 16E show a subsequent step subsequent to the step ofFIG. 15 and FIGS. 15A to 15C, showing the subsequent step similarlythereto.

FIG. 17 and FIGS. 17A to 17C show a subsequent step subsequent to thestep of FIG. 16 and FIG. 16E, showing the subsequent step similarlythereto.

FIGS. 18A and 18B each are a top plan view of the pattern of a photomaskused to form a convex-concave film by using a polygon pattern;

FIGS. 19A and 19B each are a top plan view of the pattern of a photomaskused to form a convex-concave film by using a circle pattern;

FIGS. 20A and 20B each are a top plan view of the pattern of a photomaskused to form a convex-concave film using an ellipse pattern;

FIG. 21 is a top plan view of the pattern of a photomask used to form aconvex-concave film by using a light shielding pattern;

FIG. 22 is a top plan view indicative of the pattern used in forming aconvex-concave film in the third embodiment;

FIG. 23 is a top plan view indicative of another example of the patternused in forming a convex-concave film;

FIG. 24 is a plan view indicative of the pattern used in forming aconvex-concave film in the fourth embodiment;

FIG. 25 is a sectional view indicative of an LCD device described in apatent publication;

FIG. 26A is a schematic view indicative of the definition of thedirection for the polarizing axis of a polarizing film, LC orientationdirection in the LC layer of an LCD device, and

FIG. 26B is a schematic view of the polarized state of light in thereflective area;

FIG. 27A is a schematic view indicative of the definition of thedirection for the polarizing axis of a polarizing film, and anotherexample of LC orientation direction in the LC layer of an LCD device,and

FIG. 27B is a schematic view of the polarized state of light in thereflective area;

FIG. 28 is a sectional view indicative of the LC-oriented state in theLCD device shown in FIG. 25 upon presence of applied voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, exemplary embodiments of the present invention will be describedwith reference to accompanying drawings, wherein similar constituentelements are designated by similar reference numerals.

FIG. 1A shows a schematic sectional view indicative of a pixel in an LCDdevice according to a first embodiment of the present invention. The LCDdevice 10 includes a first polarizing film 11, a counter substrate 12,an LC layer 13, a TFT substrate 14, a half-wave (λ/2) plate 18, and asecond polarizing film 15, which are consecutively arranged from thefront side of the LCD device, i.e, from a viewer side. Similar to theLCD device 200 shown in FIG. 25, the LCD device 10 is configured as atransflective type LCD device including a reflective area and atransmissive area in each pixel, and FIG. 1 shows the sectionalconfiguration in the reflective area 21.

The polarization direction (light transmission direction or lightabsorption direction) of the first polarizing film 11 and thepolarization direction of the second polarizing film 15 areperpendicular to each other. The LC layer 13 includes therein LCmolecules which are arranged such that, upon absence of applied voltage,the longer axis direction of LC molecules is aligned with thepolarization direction of the first polarizing film 11 or secondpolarizing film 15. In the following description, the definition ofdirections in the LCD device is such that the light transmission axisdirection of the first polarizing film 11 is set to 90 degrees, thepolarization direction of the second polarizing film 15 is set to 0degree, and the longer axis direction of LC molecules in the LC layer 13upon absence of applied voltage is set to 90 degrees.

In the reflective area 21 on the TFT substrate 14, a second insulatingfilm 42 is formed on an insulating film 17, and a reflection film 16 isformed on the second insulating film 42. On the reflection film 16, athird insulating film 41 is formed. The reflection film 16 reflects theexternal light incident onto the LCD device through the first polarizingfilm 11 toward the first polarizing film 11. The reflective area 21 usesthe light reflected by the reflection film 16 as a display light source.In general, to improve the scattering effect of light, the reflectionfilm 16 is so formed as to have convex portions and concave portionsthereon in the two-dimensional random arrangement. So as to realize theconvex portions and concave portions on the reflection surface, theremay be employed a configuration in which convex portions and concaveportions are formed on the second insulating film 42, and a metal filmmade of Al, Ag or an alloy thereof is arranged on the thus formed convexportions and concave portions of the second insulating film 42 as areflection film. The convex portions and concave portions may be formedby forming a two-dimensional array of convex surfaces. The LCD device 10includes a backlight source or backlight unit, not shown, disposedbehind the second polarizing film 15, and the transmissive area, notshown, uses the backlight source as a display light source.

The LC cell gap in the transmissive area is adjusted such that theretardation of the LC layer 13 assumes approximately λ/2. The expressionof “approximately λ/2” is used because, in reality, the effectiveretardation assumes λ/2 when the retardation is set to (λ/2)+α. This isbecause, upon presence of applied voltage on the LC layer 13 to rotatethe longer axis of the LC molecules therein, the LC molecules rotate atthe central part of the cell gap, while the rotation of the LC moleculesis suppressed in the vicinity of the substrates. For example, in casethe retardation of the LC layer 13 is set to Δnd=300 nm, the effectiveretardation upon presence of applied voltage thereto is set toΔndeff=λ/2=550/2=275 nm. On the other hand, in the reflective area 21,by suitably setting the height of the insulating film 17, the cell gapis adjusted so that the effective retardation of the LC layer 13 uponpresence of applied voltage thereto assumes λ/4.

On the third insulating film 41 and overlying the insulating film 17,there are formed pixel electrodes 35 to drive the LC molecules andcommon electrodes 37 to supply a reference potential. Furthermore,although not shown, pixel electrodes 35 and common electrodes 37 fordriving the LC molecules in the transmissive area are formed on the TFTsubstrate 14, corresponding to the transmissive area. The commonelectrodes 37 have a portion extending in parallel with a gate line andanother portion protruding from the first portion in the display area.The common electrode 37 is provided at a position opposing the pixelelectrode 35 on the plane of the substrate surface. Furthermore, thecommon electrode in the transmissive area is formed at a positionopposing the pixel electrode in the transmissive area on the plane ofthe substrate surface. To the common electrode of the respective areas,a drive signal is supplied having a predetermined waveform which iscommon to the respective pixels in the LCD device 10.

FIG. 1B shows the definition of the areas of the reflection film 16 andthe inclination angle α of the convex-concave surface of the reflectionfilm in this text. The reflection film 16 has a convex-concave surfacethereon, which includes a plurality of areas A (i.e. first areas) eachof which overlaps one of the electrodes 35, 37 and a plurality of areasB (i.e. second areas) each of which overlaps the gap between the pixelelectrode 35 and the common electrode 37 disposed adjacent to eachother. An inclination angle of the convex-concave surface can bemeasured between the tangential line of the convex portion of theconvex-concave surface of the reflection film 16 and a plane parallel tothe substrate surface. In this text, the inclination angle α in eacharea A or each area B is defined here by an average of the maximuminclination angles between the possible tangential lines of a convexportion in the each area and the substrate surface.

FIG. 2 shows the drive signal waveform supplied to the pixel electrodeand common electrode. In FIG. 2, the data signal shown in solid line issupplied to the pixel electrodes 35 of respective pixels, and the commonsignal shown in the dotted line is supplied to the common electrodes 37.In this example, the phase of the data signal is opposite to the phaseof the common signal, and the potential difference between the potentialof the pixel electrode 35 and the potential of the common electrode 37assumes Vd. Thus, an electric field having an intensity corresponding tothe potential difference Vd is applied to the LC layer 13 in thereflective area 21.

FIG. 3 shows a schematic view indicative of the polarized state of lightin the reflective area 21 when the signals having the waveform shown inFIG. 2 are applied to the electrodes therein. In the state in which thewaveforms shown in FIG. 2 are applied, LC molecules of the LC layer 13in the reflective area 21 have their aligned direction rotated by 45degrees from the initial state due to the electric field generatedbetween the pixel electrode 35 and common electrode 37.

As shown in FIG. 3, a 90-degree-linearly polarized light having apolarization in the longitudinal direction is passed by the firstpolarizing film 11 from the outside, and has its polarized state changedafter passing through the LC layer 13 to assume clockwise-circularlypolarized light. The clockwise-circularly polarized light is thenreflected by the reflection film 16 to assume acounterclockwise-circularly polarized light, and thecounterclockwise-circularly polarized light passes through the LC layer13 again to assume 0-degree-linearly polarized light having apolarization in lateral direction. Accordingly, the reflected light fromthe reflection film 16 is blocked by the first polarizing film 11, andthe image assumes a dark state or black in the reflective area 21.

Hereinafter, the results of investigation performed to solve theproblems in the related LCD device of the reflective type ortransflective type of the lateral-electric-field drive mode will bedescribed. The problems included a problem that the reflection contrastratio is lowered in the normally white mode, and a problem that thereflectance is lowered in the normally black mode. This investigationwas intended to find what configuration of an irregular reflection filmshould have, if LC molecules on the comb teeth electrodes do not rotatesufficiently upon presence of applied voltage. As the configuration ofthe LCD device, the LCD device shown in FIG. 1 is considered. That is,there is considered an LCD device of the reflective type ortransflective type of the lateral-electric-field drive mode which issimilar to the LCD device described in JP-2003-344837A1 (shown in FIG.25). In the LCD device shown in FIG. 1, the pixel includes a reflectionfilm 16 having a convex-concave surface in a part or all the pixel area,the reflection film 16 being formed on a convex-concave overcoat (OC)film 42 such has having a plurality of convex portions arranged in arandom two-dimensional array, and the pixel electrodes 35 and commonelectrodes 37 are formed into the comb teeth structure, which is formedon the convex-concave OC film 42 with an intervention of the reflectionfilm 16 and an interlayer dielectric film 41.

As has been pointed out in the problems to be solved, the LC moleculeson the comb teeth electrodes are not operated even upon presence ofapplied voltage in the lateral-electric-field drive mode. This leads tothe problem that the light passed by the LC molecules on the comb teethelectrodes cause noise. In view of this fact, it is concluded that thereflected light of the light passing through the comb teeth electrodesis excluded from the viewing point of the viewer after the reflection.That is, since the reflected direction of light passing through theelectrodes and the reflected direction of light passing the gap betweenthe electrodes overlap each other, the reflectance upon display of darkstate cannot be lowered, to thereby reduce the contrast ratio.Therefore, it is concluded that the contrast ratio in the reflectionmode can be improved by preventing the reflected direction of lightpassing through the electrodes and the reflected direction of lightpassing through the gap between the electrodes from overlapping eachother.

LC molecules disposed on the gap between the electrodes rotate on theplane of the substrate surface upon presence of applied voltage, whereasLC molecules on the electrodes do not rotate on the plane of thesubstrate surface upon presence of applied voltage. In view of thisfact, the light passing through the gap between the electrodes isreflected in the direction toward the viewer by using the reflectionfilm, whereas the light passing the electrodes is reflected in thedirection other than the viewer by using the reflection film to improvethe contrast ratio on the viewer side, which can increase thevisibility. In this embodiment, the direction of the viewer side isdefined as an angle within a predetermined angle range from a directionperpendicular to the substrate surface, for example, an angle range of 0degree to 15 degrees for the incident light having an incident angle 30degrees. As a direction other than the viewer, the direction in whichlight is reflected under the mirror reflection with respect to thesubstrate surface is considered. That is, an emitting angle of 30degrees is considered with respect to the incident angle of 30 degrees.The direction of the mirror reflection is referred to as the speculardirection hereinafter.

FIG. 4 shows the travelling state of light in the LCD device. Ingeneral, in an LCD device provided with the reflection mode, it isconsidered that a viewer will observe the incident light incident on theLCD device at an incident angle of 30 degrees by recognizing theemitting light reflected at a reflection angle of approximately 0 degreeto 15 degrees. The reason is that observation of light incident at anincident angle of 30 degrees by recognizing the emitting light reflectedat an angle of 30 degrees or the vicinity thereof will lead toundesirable observation of reflected light source, which causes theviewer to observe the reflected light source, to feel difficulty inrecognition of the displayed image. This situation is shown by asimplified structure shown in FIG. 4. Assuming that the incident angleof light is 30 degrees, the relationship between the inclination angle αof the reflection film 16 and the emitting angle β of the emitting lightgenerated by reflection of the incident light can be approximated by theexpression (4) by combining the expressions (1) to (3).n1·sin(30 degrees)=n2·sin θ2  (1)θ3=θ2−2·α  (2)n1·sin β=n2·sin θ3  (3)α={sin⁻¹ [(n1/n/2)·sin β]−sin⁻¹[(n1/n/2)·sin(30 degrees)]}/2  (4)

It is assumed that the refractive index of the air is n1=1.0, and therefractive index of the third insulating film 41 on the reflection film16 is n2=1.5. In order to reflect the light incident at 30 degreestoward the range of 0 degree to 15 degrees, i.e., direction of theviewer, it is sufficient that the inclination angle of theconvex-concave surface of the reflection film 16 is controlled so thatthe angle components in the range of 4.7 degrees to 9.1 degreesincrease, by using the expression (4). In addition, in order to reflectthe light incident at 30 degrees toward the range of 20 degrees to 30degrees, i.e., in the specular reflection direction, it is sufficientthat the inclination angle of the convex-concave surface of thereflection film 16 is controlled so that the angle components in therange of 0 degree to 2.9 degrees increases, by using the expression (4).For this purpose, the average inclination angle of an area of theconvex-concave surface overlapping the electrodes is selected smallerthan the average inclination angle of another area of the convex-concavesurface overlapping the gap between the electrodes. In this structure,the light incident at 30 degrees on the electrodes is reflected by thearea of the convex-concave surface toward the viewer, whereas the lightincident at 30 degrees on the gap between the electrodes is reflectedtoward the specular reflection direction.

From expression (4), the inclination angle α of the convex-concavesurface of the reflection film 16 depends on the refractive index of thethird insulating film 41. Thus, it is sufficient that the inclinationangle of the respective areas be designed based on the refractive indexof the insulating film 41 to be used. Specifically, it is sufficientthat the inclination angle of both the areas be made smaller, if therefractive index of the insulating film is smaller than 1.5. On theother hand, if the refractive index of the insulating film is largerthan 1.5, the inclination angle of both the areas be made larger. Infact, the inclination angle of the convex-concave surface of thereflection film 16 changes continuously. As a method to measure theinclination angle α, there may be employed a method in which the heightof the surface of the reflection film is measured using an atomic forcemicroscope (AFM), and the absolute value of the inclination or slopebetween two neighboring points is approximated to the inclination angle.

Based on the above principle, the present embodiment uses aconfiguration wherein the incident light passing through the comb teethelectrodes, on which the LC molecules are not rotated, and reflected bythe reflective film is prevented from being observed by a viewer. Forthis purpose, it is required that the light be intensively orcollectively reflected in the specular direction in which the directionof 30 degrees is the central direction, and not reflected toward therange of angle between 0 degree and 15 degrees. In order to realize thisfunction, the present embodiment uses a measure that the inclinationangle of an area of the convex-concave surface of the reflection filmoverlapping the comb teeth electrodes is different from the inclinationangle of another area of the convex-concave surface in the areaoverlapping the gap between the comb teeth electrodes. Specifically,from the above description, the average inclination angle of the firstarea of the convex-concave surface of the reflection film overlappingthe comb teeth electrodes is set to the range of 0 degree to 2.9degrees, to control the emitting angle of the reflected light in thespecular direction. On the other hand, the average inclination angle ofthe second area of the convex-concave surface of the reflection film inthe area overlapping the gap of the comb teeth electrodes is set toapproximately 4.7 degrees to 9.1 degrees, to control the emitting angleof the reflected light within the range of 0 degree to 15 degrees, inwhich range the viewer observes the reflected light. The averageinclination angle is obtained by averaging the inclination angles withinthe specified area, i.e., first area or second area. For example, theremay be employed a method in which values measured and calculated by theAFM is averaged to obtain the average inclination angle. A reflectionfilm having a convex-concave surface may be such that a plurality ofconvex portions are arranged in a two-dimensional array on thereflection film.

For forming the inclination angle of the reflection film 16 in the areaoverlapping the electrodes different from that in the area overlappingthe gap between the electrodes, a least number of convex portions are tobe formed on the comb teeth electrodes, and the area of the reflectionsurface of the reflection film is separated in terms of the magnitude ofthe inclination angle into an area A overlapping the comb teethelectrodes and an area B overlapping the gap between the comb teethelectrode. With respect to the pattern of the convex-concave surface,the visibility was deteriorated due to the interference if a regularconvex-concave surface such as corrugate pattern shown in FIG. 5 or FIG.6 is used wherein convex portions 51 and concave portions 52 areregularly arranged. Thus, a convex-concave pattern such as shown in FIG.7 and FIG. 8 is used wherein the extending direction of convex portions51 is randomly changed to form triangular concave portions 52. Thepattern shown in FIG. 7 is such that the convex-concave surface isformed on the area overlapping the electrodes 35, 37 as well as on thearea overlapping the gap between the electrodes 35, 37, similarly toFIG. 5. The pattern shown in FIG. 8 is such that convex portions 51 arenot formed on the area overlapping the electrodes 35, 37. By forming theconvex-concave surface on the reflection film 16 by using theconvex-concave pattern, it is studied to what extent the contrast ratioin the reflection mode and in the normally white mode is improved.

In evaluating the leakage light, it is sufficient that the ratio of thereflectance upon display of dark state and the reflectance upon displayof bright state be evaluated, or the contrast ratio be evaluated. Inperforming the evaluation, as shown in FIG. 9, the direction of 0 degreeto 15 degrees from the perpendicular to the substrate surface is definedas the observer side and set for the light receiving angle of a photodetector. A direction of 30 degrees opposite to the light receivingangle with respect to the perpendicular to the substrate surface is setas the incident angle of the incident light. A projector is used as alight source for the incident light, which is reflected by the LCDdevice 10 and then measured by the photo detector for evaluation. Astandard white plate (WS-3 manufactured by TOPCOM) which is formed bybarium sulfate is used as the light source, and the relative reflectanceis measured with the reflectance at the light receiving angle of 0degree being 100%.

The contrast ratio is measured using an LCD device including areflection film similar to the conventional reflection film having aconvex-concave surface wherein the inclination angle is uniform betweenthe area overlapping the electrodes and the area overlapping the gapbetween the electrodes. The resultant contrast ratio was approximately5:1. On the other hand, the evaluation was also performed using areflection film having a convex-concave surface in the area overlappingthe gap between electrodes and having a uniform surface on theelectrodes, wherein the inclination angle of the convex-concave surfaceis different between the area A and area B. The resultant contrast ratiowas as high as 13:1. Thus, it was confirmed that the configurationwherein the inclination angle of the convex-concave surface is differentbetween the area A and the area B, and wherein the light passing throughthe electrodes is reflected collectively to the specular reflectiondirection provided an improved contrast ratio and excellent visibility,due to little reflection amount into the receiving angle range of 0 to15 degrees.

A process of manufacturing the TFT substrate 14 will be described withreference to FIGS. 10 to 17 together with sectional views taken alongrespective lines specified in those drawings. In these drawings, thedrawings having a figure number without an alphabet are top plan viewsof the TFT substrate, whereas the drawings having a figure number withan alphabet are sectional views taken along line denoted by the alphabetshown in the corresponding top plan view.

Firstly, a gate line 31, a first common electrode line 37 a, and asecond common electrode line 38 a are formed on a transparent substrateby using a pattern shown in FIG. 10. The reflective area 21,transmissive area 22, and vicinity of the boundary between thereflective area 21 and the transmissive area 22 are shown in FIG. 10A toFIG. 10C. In order to supply a potential to the reflection film 16 inthe reflection area 21, the first common electrode line 37 a is soformed as to protrude in the display area. Subsequently, the gate line31, first common electrode line 37 a, and second common electrode line38 a are covered by the insulating film 17 (FIG. 1).

Next, as shown in FIG. 11, a semiconductor layer 39 to form therein theTFTs is formed. Sectional views of respective parts are shown in FIG.11A to FIG. 11D. During forming the semiconductor layer 39, as shown inFIG. 11B, the semiconductor layer 39 is so formed as to overlap the gateline 31. Subsequently, using a pattern shown in FIG. 12, pixel electrodelines 35 a, 36 a to be connected to the source/drain of the TFTs areformed. At this step, the reflective area 21, transmissive area 22, andvicinity of the boundary between the reflective area 21 and thetransmissive area 22 are also shown.

In the reflective area 21, the first common electrode line 37 a isformed between adjacent pixel electrode lines 35 a. At this step, thefirst common electrode line 37 a is formed such that the area ratiobetween the pixel electrode line 35 a and the first common electrodeline 37 a assumes 1:1 in the display area. This is for the purpose ofsupplying the intermediate potential between the pixel electrode 35 andthe common electrode 37 to the reflection film 16, to be formed later,during displaying an image. After forming the first common electrodeline 37 a and second common electrode line 38 a, the insulating film 17is formed thereon.

Thereafter, a convex-concave overcoat (OC) film 42 is formed, as asecond insulating film, as shown in FIG. 13. As shown in FIG. 13A toFIG. 13D, the convex-concave OC film 42 is so formed as to haveconvex-concave surface wherein a plurality of convex portions are formedto define the convex potions and concave portions. In this step,photosensitive resin is coated on the substrate, and the photosensitiveresin is exposed to light by using a photomask formed by using the maskpattern such as shown in FIG. 5, an exposed portion of thephotosensitive resin is removed by development, and the developedphotosensitive resin is subjected to a burning treatment to form theconvex-concave OC film 42. In the thus formed convex-concave OC film 42,the inclination angle has different components between the area Acorresponding to the electrodes 35, 37 and the area B corresponding tothe gap between adjacent two of the electrodes 35, 37. An Al layer isthen formed on the thus formed convex-concave OC film 42, and patternedto form the reflection film 16 in the reflective area 21 by using apattern shown in FIG. 14. The resultant reflection film 16 has aconvex-concave surface which reflects the convex-concave surface of theunderlying convex-concave OC film 42. The reflective area 21,transmissive area 22, and vicinity of the boundary between thereflective area 21 and the transmissive area 22 are also shown in FIG.14A to FIG. 14D.

After forming the reflection film 16, a planarization OC layer 41 isformed as a third insulating film by using a pattern shown in FIG. 15.The planarization OC layer 41 provides a step difference in the vicinityof the boundary between the reflective area 21 and the transmissive area22, as shown in FIG. 15A to FIG. 15D. The planarization OC layer 41adjusts the cell gap between both the areas. Thereafter, contact holes43 are formed in the insulating film 17 covering the pixel electrodelines 35 a, 36 a and common electrode lines 37 a, 38 a, as shown in FIG.16, whereby pixel electrode lines 35 a, 36 a and common electrode lines37 a, 38 a are exposed, as shown in FIG. 16E.

After forming the contact holes 43, the pixel electrodes 35, 36 andcommon electrodes 37, 38 are formed on the planarization OC layer 41, byusing a pattern shown in FIG. 17. The reflective area 21, transmissivearea 22, and vicinity of the boundary between the reflective area 21 andthe transmissive area 22 are shown in FIG. 17A to FIG. 17C. In the stepof forming the pixel electrodes 35, 36 and common electrodes 37, 38, therespective electrodes, pixel electrode lines 35 a, 36 a, and commonelectrode lines 37 a, 38 a are connected together via the contact holes.By using the above process, the TFT substrate 14 to be used in atransflective type LCD device 10 in this embodiment is produced.

Next, the advantages of the above embodiment will be described. In theembodiment, the inclination angle of the convex-concave surface of thereflection film 16 overlapping the electrodes is different from thatoverlapping the gap between the electrodes in the LCD device 10 of thelateral-electric-field drive mode and including the reflection mode ofthe normally white mode. By suitably setting the inclination angle in anarea corresponding to the electrodes and the inclination angle in anarea corresponding to the gap between the electrodes, the light whichpasses through the gap between the electrodes and reflected by theconvex-concave surface of the reflection film is emitted in the range ofthe received angle of 0 degree to 15 degrees for the photo detector, andlight which passes the electrodes, where LC molecules are not rotated,are reflected toward the specular reflection direction range having acenter at the direction of 30 degrees from the perpendicular. Theprevention of light passing through the electrodes from emitting in thereceived range of 0 degree to 15 degrees improves the contrast ratio ascompared to the case where the inclination is uniform between theelectrodes and the gap between the electrodes, to thereby improve thevisibility.

In the above embodiment, the pattern shown in FIG. 7 or FIG. 8 is usedfor forming a triangular pattern on the convex-concave OC film. However,in an alternative, as shown in FIGS. 18A and 18B, a pattern may be usedin which sides of polygons other than triangles correspond to convexportions 51 (FIG. 18B) or concave portions 52 (FIG. 18A). Furthermore, apattern using circles shown in FIGS. 19A and 19B and a pattern usingellipses shown in FIGS. 20A and 20B may be employed. When employingthese patterns, areas encircled by the circles or ellipses maycorrespond to convex portions 51 (FIGS. 19A and 20A), or areas encircledby the circles or ellipses and may to correspond to concave portions 52(FIGS. 19B and 20B). Furthermore, a combination pattern including aplurality of these patterns may be employed to configure theconvex-concave surface of the reflection film 16. Moreover, patternsother than these patterns may be employed so long as the patterns canobtain desired reflection characteristics, in which the convex-concavesurface is provided in an area overlapping the gap between theelectrodes 35, 37, and the convex-concave surface is not provided in anarea overlapping the electrodes 35, 37. Moreover, in the abovedescription, a photomask that forms the convex-concave pattern is usedfor removing the pattern from the portion corresponding to theelectrodes. However, as shown in FIG. 21, a photomask which has a lightshielding pattern 53 on the portion corresponding to the electrodes 35,37 may be employed as well to lower the inclination angle.

Next, a second embodiment will be described. This embodiment is similarto the first embodiment except that the display mode is the normallyblack mode in the present embodiment. Also in this embodiment, it isstudied that the convex-concave surface is scarcely formed to overlapthe comb teeth electrodes, and the inclination angle of theconvex-concave reflection film is different between the area Aoverlapping the electrodes and the area B overlapping the gap betweenthe electrodes. The pattern used in the present embodiment is similar tothat in the first embodiment. That is, the convex-concave pattern shownin FIG. 7 and FIG. 8 in which sides of randomly arranged trianglesconfigure the convex portions.

By using different the inclination angles of the convex-concave surfaceof the reflection film between the area A and area B, it wasinvestigated how the reflectance in the reflection mode is changed inthe case of the normally block mode. The result is shown in the table 1as listed below. In this table 1, the average inclination angle iscalculated for the part where the portion corresponding to theelectrodes is subjected to planarization and the part where the portioncorresponding to the electrodes is subjected to planarization. In caseof the same average inclination angle, planarization of the partcorresponding to the electrodes provides a higher reflectance. Thisindicates that the formation of the convex-concave surface increases thelight components of the inclination angle reflected on the gap betweenthe electrodes to contribute a bright image, that is, components in therange of 5 degrees to 9 degrees. The increase is obtained by disposingthe convex portions having a higher inclination angle on the electrodeswith a higher density.

TABLE 1 Average inclination angle and relative reflectance RelativeReflectance on Light Receiving Angle of 10 degrees Average Inclination 67.5 9 Angle (deg.) Planarization Ratio 14.8 19.3 13.4 on Electrodes (%)Ratio of 13.3 15.6 7.9 Convex-Concave Portion (%)

From the above-described results, it is also confirmed in thisembodiment of the normally black mode that planarization of theconvex-concave OC film in the area overlapping the electrodes improvesthe luminance of the bright state. In addition, it is also confirmedthat the bright state image provided by absence of applied voltage canneglect the influence by the planarization of the reflection film in thearea overlapping the electrodes. This fact means that the improvement ofthe reflectance upon display of bright state improves the contrast ratioand achieves a higher contrast ratio.

Next, a third embodiment will be described. In the first and secondembodiments, a higher contrast ratio is obtained by removing theconvex-concave surface of the reflection film overlapping theelectrodes. On the other hand, in this embodiment, the inclination angleof the convex-concave surface of the reflection film is reduced in thearea overlapping the electrodes by arranging patterns in the form ofdots in the area overlapping the gap between the electrodes. Inaddition, patterns in the form of dots, which are smaller than the dotsformed in the area overlapping the gap between the electrodes, areprovided in the area overlapping the electrodes. Those configurationsprovide a smaller inclination angle of the convex-concave surface of thereflection film in the area overlapping the electrodes. Otherconfigurations are similar to those in the first and second embodiments.

FIG. 22 shows a pattern of convex-concave surface of the reflectionfilm. This pattern is such that rectangular dot patterns are provided inthe area overlapping the gap between the electrodes 35, 37, and agray-tone film 54 including rectangular dot patterns having a smallersize are also provided in the area overlapping the electrodes 35, 37. Inthis figure, the rectangular dot patterns may be replaced by dotpatterns having different shape, such as circular dot patterns,elliptical dot patterns or polygonal dot patterns. These dot patternsallow the portion of the convex-concave surface to be more planarized onthe electrode.

Formation of the convex-concave surface of the reflection film by usingthe patterns shown in FIG. 22 reduces the inclination angle, which isformed between the planarized portion of the reflection film overlappingthe electrodes and other peripheral portion and thus extend parallel tothe electrodes, as compared with the case of using patterns which removeconvex-concave surface in the area overlapping the electrodes. Thus, thereflectance and the contrast ratio are not reduced with respect to theangle range of 0 degree to 15 degrees, and the light incident from theother angle range is not scattered to achieve an excellent visibility.In FIG. 22, small dot patterns are arranged on the portion correspondingto the electrodes 35, 37. However, a half-tone mask using asemi-transmissive film may be used instead, as shown in FIG. 23.

Next, a fourth embodiment will be described. FIG. 24 shows a patternused for forming a convex-concave surface on the reflection film in thisembodiment. Other configurations are similar to those in the aboveembodiments. In this embodiment, a half-tone mask 55 is provided on atleast the portion corresponding to the electrodes 35, 37. In thisconfiguration, the half-tone mask 55 formed only in the area overlappingthe electrodes 35, 37 and combined with the conventional convex-concavesurface of the reflection film reduces the amount of exposure light onthe convex-concave surface overlapping the electrodes 35, 37 compared tothe convex-concave surface overlapping the gap between the electrodes.This reduces the average inclination angle in the area overlapping theelectrodes, whereby the light passed by the electrodes can be reflectedinto the specular reflection direction, thereby improving the contrastratio.

As described heretofore, in the respective embodiments of the presentinvention, inclination angle of the reflection film is different betweenthe area corresponding to the electrodes and the area corresponding tothe gap between the electrodes, whereby the light passed by theelectrodes, on which the LC molecules are not rotated, is reflectedtoward the specular reflection direction and the vicinity thereof. Thisimproves the contrast ratio up to a higher value of 13:1 or more ascompared to the case of conventional normal white mode achieving acontrast ratio of around 3:1 at the maximum. In addition, in the case ofnormal black mode, as shown in Table 1, a maximum of 70% reflectance canbe achieved for the same average inclination angle (9 degrees), and alsoa 23% reflectance improvement can be achieved at the average inclinationangle of 7.5 degrees at which the reflectance assumes a maximum, andalso the contrast ratio can be improved.

While the invention has been particularly shown and described withreference to exemplary embodiment and modifications thereof, theinvention is not limited to these embodiment and modifications. It willbe understood by those of ordinary skill in the art that various changesin form and details may be made therein without departing from thespirit and scope of the present invention as defined in the claims.

1. A photomask used for forming a convex-concave surface on a reflectivearea of liquid crystal display (LCD) device including comb teethelectrodes for driving liquid crystal (LC) molecules in alateral-electric-field drive mode, the reflective area in at least apart of a pixel, wherein said photomask comprises: a first areacorresponding to, in said reflective area, an area under each of saidcomb teeth electrodes, and a second area corresponding to, in saidreflective area, and area between adjacent electrodes of said comb teethelectrodes, said second area being present between adjacent portions ofsaid first area, wherein said second area has a predetermined patternformed by at least one light transmitting area and at least on lightabsorbing area absorbing more light than said at least one lighttransmitting area, and said first area has a uniform light transmittingproperty is used for forming said convex-concave surface on saidreflection film, and has no convex-concave pattern in an areaoverlapping said electrodes, wherein said first area comprises ahalf-tone mask.
 2. A photomask used for forming a convex-concave surfaceon a reflective area of liquid crystal display (LCD) device includingcomb teeth electrodes for driving liquid crystal (LC) molecules in alateral-electric-field drive mode, the reflective area in at least apart of a pixel, wherein said photomask comprises: a first areacorresponding to, in said reflective area, an area under each of saidcomb teeth electrodes, and a second area corresponding to, in saidreflective area, and area between adjacent electrodes of said comb teethelectrodes, said second area being present between adjacent portions ofsaid first area, wherein said second area has a predetermined patternformed by at least one light transmitting area and at least on lightabsorbing area absorbing more light than said at least one lighttransmitting area, and said first area has a uniform light transmittingproperty is used for forming said convex-concave surface on saidreflection film, and has no convex-concave pattern in an areaoverlapping said electrodes, wherein each of said at least one lighttransmitting area of said second area has a triangular shape.
 3. Aphotomask used for forming a convex-concave surface on a reflective areaof a liquid crystal display (LCD) device including comb teeth electrodesfor driving liquid crystal (LC) molecules in a lateral-electric-fielddrive mode, the reflective area in at least a part of a pixel, whereinsaid photomask comprises: a first area corresponding to, in saidreflective area, an area under each of said comb teeth electrodes, and asecond area corresponding to, in said reflective area, an area betweenadjacent electrodes of said comb teeth electrodes, said second areabeing present between adjacent portions of said first area, wherein saidsecond area comprises a light absorbing area and a light transmittingarea, wherein said light absorbing area comprises a plurality of dotsarranged in said light transmitting area, said light absorbing areaabsorbing more light than said light transmitting area, and wherein saidfirst area comprises a grey-tone area and a light transmitting area,wherein said grey-tone area comprises a plurality of dots arranged insaid light transmitting area, wherein said plurality of dots of saidgrey-tone area are smaller than said plurality of dots of said lightabsorbing area.